The present invention relates to novel anti-infectives. Specifically, the present invention involves novel HCV inhibitors.
First identified by molecular cloning in 1989 (Choo et al., 1989), hepatitis C virus (HCV) is now widely accepted as the most common causative agent of post-transfusion non A, non-B hepatitis (NANBH) (Kuo et al., 1989). Due to its genome structure and sequence homology, this virus was assigned as a new genus in the Flaviviridae family, along with the other two genera, flaviviruses (such as yellow fever virus and Dengue virus types 1-4) and pestiviruses (such as bovine viral diarrhea virus, border disease virus, and classic swine fever virus) (Choo et al., 1989; Miller and Purcell, 1990). Like the other members of the Flaviviridae, HCV is an enveloped virus containing a single strand RNA molecule of positive polarity. The HCV genome is approximately 9.6 kilobases (kb) with a long, highly conserved, noncapped 5xe2x80x2nontranslated region (NTR) of approximately 340 bases which functions as an internal ribosome entry site (IRES) (Wang and Siddiqui, 1995). This element is followed by a region which encodes a single long open reading frame (ORF) encoding a polypeptide of xcx9c3000 amino acids comprising both the structural and nonstructural viral proteins. Upon entry into the cytoplasm of the cell, this RNA is directly translated into a polypeptide of xcx9c3000 amino acids comprising both the structural and nonstructural viral proteins. This large polypeptide is subsequently processed into the individual structural and nonstructural proteins by a combination of host and virally-encoded proteinases (reviewed in Rice, 1996). Following the termination codon at the end of the long ORF, there is a 3xe2x80x2NTR which roughly consists of three regions: an xcx9c40 base region which is poorly conserved among various genotypes, a variable length poly (U)/polypyrimidine tract, and a highly conserved 98 base element also called the xe2x80x9c3xe2x80x2Xtailxe2x80x9d (Kolykhalov et al., 1996; Tanaka et al., 1995; Tanaka et al., 1996; Yamada et al., 1996). The 3xe2x80x2NTR is predicted to form a stable secondary structure which is essential for HCV growth in chimps and is believed to function in the initiation and regulation of viral RNA replication.
Infection with HCV is a major cause of human liver disease throughout the world with seroprevalence in the general population ranging from 0.3 to 2.2% (van der Poel et al., 1994) to as high as xcx9c10-20% in Egypt (Hibbs et al., 1993). HCV is most commonly transmitted via blood (Alter et al., 1993). Of these initial infections, an estimated 30% are symptomatic. However, more than 85% of all infected individuals become chronically infected (3.9 million current chronic infections in US, 170 million chronic infections worldwide, estimated 33,200 new cases in 1994 in US). Chronic HCV infection accounts for 30% of all cirrhosis, end-stage liver disease, and liver cancer in the U.S. Of the total chronic cases in the US, greater than 118,000 will go on to develop hepatocellular carcinoma (HCC) (which represents xe2x89xa725% of all liver cancers) as a direct result of HCV infection (reviewed in Hoofnagle, 1997; Seeff, 1997). There are 8,000-12,000 deaths per year in the US currently attributed to HCV infection, and treatment costs were estimated at 600 million for 1992 in the US. The CDC estimates that the number of deaths due to HCV will increase to 38,000/yr. by the year 2010.
Due to the high degree of variability in the viral surface antigens, existence of multiple viral genotypes, and demonstrated specificity of immunity, the development of a successful vaccine in the near future is unlikely. Although initially therapy consisted of interferon alone, combination therapy of interferon alpha-2b (xe2x96xa1-IFN, 3 million units injected subcutaneously three times weekly) with ribavirin (1-1.2 gms twice daily orally) for either 24 or 48 weeks is currently the most efficacious approved therapy for the treatment of chronic HCV infection. Schering-Plough alone reported over $430 million in sales for interferon alone in 1998 specifically for HCV therapy. The response and sustained response rates for combination therapy were better than interferon alone (80% initial response for combo vs. 46% for IFN alone; and 30-50% sustained response for combo vs. 5-13% for IFN alone). However, there were still many adverse side effects associated with combination therapy (flu-like symptoms, leukopenia, thrombocytopenia, depression, etc. from interferon), as well as anemia induced by ribavirin (reviewed in Lindsay, 1997). Furthermore, this therapy was still less effective against infections caused by HCV genotype 1 which constitutes xcx9c75% of all HCV infections in the developed markets (as opposed to other HCV genotypes). Analogous to therapy for HIV infection, combination therapy (i.e. IFN plus antiviral or antiviral cocktail) is likely to be the most efficacious therapy.
In the US, an estimated 3.9 million Americans are infected with HCV. Although only 30% of acute infections are symptomatic,  greater than 85% of infected individuals develop chronic, persistent infection. There are 8,000-10,000 deaths per year in the US currently attributed to HCV infection, and treatment costs are estimated at  greater than 600 million/yr. (1992 CDC estimate for US). Worldwide over 170 million people are estimated to be infected chronically. HCV infection is responsible for 40-60% of all chronic liver disease and 30% of all liver transplants. A vaccine is unlikely due to hypervariable surface antigens and demonstrated specificity of immunity.
Currently, there are no HCV antiviral agents available, with alpha-interferon (alone or in combination with ribavirin) being the only approved treatment. Many adverse side effects are associated with therapy (flu-like symptoms, leukopenia, thrombocytopenia, depression, anemia, etc.); only xcx9c50-80% of the patients respond (reduction in serum HCV RNA levels, normalization of liver enzymes); however, of those treated, 50-70% relapse within 6 months of cessation of therapy.
The NS5B protein (591 amino acids, 65 kDa) of HCV (Behrens et al., 1996), encodes an RNA-dependent RNA polymerase (RdRp) activity and contains canonical motifs present in other RNA viral polymerases. The NS5B protein is fairly well conserved both intratypically (one type 1b isolate vs. another type 1b isolate, xcx9c95-98% aa identity) and intertypically (type 1a vs. type 1b, xcx9c85% aa identity). The essentiality of the HCV NS5B RdRp activity for the generation of infectious progeny virions has been formally proven in chimpanzees (A. A. Kolykhalov et al..abstract, 1999) and inhibition of NS5B RdRp activity is therefore predicted to be antiviral for HCV infection, and inhibition of RNA replication would be expected to cure infection.
Based on the foregoing, there exists a significant need to identify synthetic or biological compounds for their ability to inhibit HCV.
The present invention involves compounds represented hereinbelow, pharmaceutical compositions comprising such compounds and methods of using the present compounds.